Troubleshooting
Problem
In a SAN tape environment, Control Path Failover enables multiple physical control paths, providing automatic failover to an alternative control path when an error occurs on one path. Data Path Failover provides a failover mechanism which allows multiple redundant paths in a SAN environment. Control Path Failover has support at V7R1 and above. Data Path Failover is now supported on i OS at V7R2 and later releases ... Manual failover was introduced at V7R2 TR2, automatic failover was added at V7R2 TR3 and V7R3. Check the Tape Multipath doc on the IBM Removable Media for IBM i Wiki pages listed below.
Resolving The Problem
In a SAN tape environment, Control Path Failover enables multiple physical control paths, providing automatic failover to an alternative control path when an error occurs on one path. Data Path Failover provides a failover mechanism which allows multiple redundant paths in a SAN environment. Control Path Failover has support at V7R1 and above. Data Path Failover is now supported on i OS at V7R2 and later releases ... Manual failover was introduced at V7R2 TR2, Automatic failover was added at V7R2 TR3 and V7R3. Check the Tape Multipath doc on the IBM Removable Media for IBM i Wiki page listed below for rules and restrictions.
Control Path and Data Path Failover
When saving to a tape library, data flows across two channels: the data path and the control path. The actual data travels along the data path. The tape library control commands such as "mount tape", "eject tape", "inventory library", and so on flow along the control path. In all libraries except the 3494, the control path and data path share the same cable.
Control Path Failover
IBM i supports control path failover on systems that are running IBM i 7.1 or higher and using IOP-less fibre cards for their tape or virtual tape. If a save is running and the IBM i detects a problem with the control path it is using, it will automatically start sending the library commands down another control path that is attached to the same fibre port and is associated with another drive in the same tape library. The save will continue without interruption. If multiple control paths fail, the save will continue to failover until there are no more operational control paths. Note that this function is not able to failover to a control path on a different fibre port or a different library.
Data Path Failover
IBM i does now offer data path failover on newer tape library or virtual tape library. Manual failover is available at V7R2 TR2 (automatic failover at V7R2 TR3 and V7R3) and above with certain limitations depending on the version/release of the i OS, the tape drive/library technology and other restrictions listed in the document linked below. However, even with an unsupported multipath configuration .. if a data path were to fail during a save, IBM i and BRMS have functions to make it easier to restart the backup on another drive if one is available or after fixing the hardware issue.
The Tape Multipath doc and more detailed information can be found in IBM Removable Media for IBM i Wiki pages at the following site:
https://www.ibm.com/support/pages/node/1115205
Control Path and Data Path Failover
When saving to a tape library, data flows across two channels: the data path and the control path. The actual data travels along the data path. The tape library control commands such as "mount tape", "eject tape", "inventory library", and so on flow along the control path. In all libraries except the 3494, the control path and data path share the same cable.
Control Path Failover
IBM i supports control path failover on systems that are running IBM i 7.1 or higher and using IOP-less fibre cards for their tape or virtual tape. If a save is running and the IBM i detects a problem with the control path it is using, it will automatically start sending the library commands down another control path that is attached to the same fibre port and is associated with another drive in the same tape library. The save will continue without interruption. If multiple control paths fail, the save will continue to failover until there are no more operational control paths. Note that this function is not able to failover to a control path on a different fibre port or a different library.
Data Path Failover
IBM i does now offer data path failover on newer tape library or virtual tape library. Manual failover is available at V7R2 TR2 (automatic failover at V7R2 TR3 and V7R3) and above with certain limitations depending on the version/release of the i OS, the tape drive/library technology and other restrictions listed in the document linked below. However, even with an unsupported multipath configuration .. if a data path were to fail during a save, IBM i and BRMS have functions to make it easier to restart the backup on another drive if one is available or after fixing the hardware issue.
The Tape Multipath doc and more detailed information can be found in IBM Removable Media for IBM i Wiki pages at the following site:
https://www.ibm.com/support/pages/node/1115205
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Historical Number
476994705
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Document Information
Modified date:
17 February 2021
UID
nas8N1013897
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